On the nature of the mesoscale circulations at a kata-cold front

A series of dropwindsondes released over the sea during the FRONTS 92 experiment is analysed to reveal the mesoscale structure of a kata-cold front characterised broadly by a dry airstream over-running a warm moist boundary layer. The front had a multiple structure with two main surface fronts and this paper is concerned with the detailed structure of one of the surface cold fronts. Two kinds of circulations are shown to coexist at such a front: vertical convection and a slantwise circulation. The slantwise circulation is a feature not normally resolved by conventional observations of kata-cold fronts: it is shown to be a small-scale version of the rearward-sloping ascent encountered in ana-cold fronts. Much of the slantwise circulation was cloud-free but where it impinged upon the boundary layer it triggered the development of a narrow band of convective cloud, the tops of which extended downstream within air that was overtaking the front.